In many applications it may be advantageous to have the ability to determine a position of a mobile device. Position location may be helpful for navigation, tracking, or orientation applications. The continual advancement of the performance of portable electronics, particularly the advancements in the performance of processors, allows position location capabilities to be added in a variety of devices.
For example, it may be desirable for an operator of a mobile telecommunications system such as a cellular telecommunications system to be able to determine the position of a mobile handset during communication with a base transceiver station (BTS) of the system. A system operator may desire position location capabilities, for example, to satisfy the U.S. Federal Communications Commission (FCC) E911 emergency position location mandate.
Mobile devices may implement one or more position location techniques depending on the position location signaling methods used in the position location system. For example, a mobile device may use time of arrival (TOA), time difference of arrival (TDOA), advanced forward link trilateration (AFLT) or some other position location technique. Examples of position location systems include those that are based on the Global Positioning System (GPS), those that augment the GPS system with terrestrial based beacons such as Assisted GPS systems, and terrestrial based beacon position location systems.
Most terrestrial ranging systems incorporate a pseudo noise (PN) code in a direct sequence spread spectrum configuration. A mobile device can identify a particular source, in part, by correlating a received PN spread signal with an internally generated version. Unfortunately, PN codes typically exhibit modest cross correlation properties unless very long PN codes are used. However, the use of long PN codes increase the complexity, bandwidth, or time required to obtain a position location fix. Additionally, because a mobile station in a terrestrial based system can receive widely disparate signal powers, even relatively low cross correlation properties can interfere with the mobile station's ability to identify signal sources.
Therefore, it is desirable to have a position location signaling technique, system, and device that allow for high performance position location in a variety of conditions and yet may be implemented in a practical manner.